This project focuses on long-term consequences of individual differences in physical, social, and affective functioning. One study is concerned with the ways certain signals of arousal or irritability in the first months of life are related to measures of the child's temperament, emotional expressiveness, and physiology at later ages. We found significant developmental increases in mean heart period, with stress- related decreases in heart-rate variability and increases in heart rate. Cortisol levels increased with age, became more individually characteristic, and varied as a function of diurnal rhythms. Individuals differences in positive and negative responding to a series of emotion- eliciting stimuli were reliable and stable over time. Although mothers' perceptions of infant temperament were also highly stable, they were unrelated to observational measures of facial expressiveness. Measures of behavioral synchrony in the home predicted differences in the subsequent security of attachment. In a second project, we are studying the effects of maternal behavior, maternal characteristics, family patterns, and infant characteristics on the socioemotional development of upper-middle class Euro-American and lower-class Central American immigrants, developing culturally-sensitive criteria for evaluating normative social behavior and development. Regardless of social or ethnic background, mothers spent a considerable amount of time in discrete activities such as feeding, caring for, and playing with their infants. Although fathers' presence did not seem to affect the amount of time infants spent in discrete activities, it did influence the time parents spent in mutual attention and vocalization with their infants. Individual differences in maternal sensitivity while feeding infants were stable over time.